From 632566f6c3115826f81fe3b013787d8b3a2fe5f1 Mon Sep 17 00:00:00 2001
From: "E. Almqvist" <elalmqvist@gmail.com>
Date: Sat, 31 Jul 2021 23:16:52 +0200
Subject: [PATCH] Disk read error refactor

---
 src/bios/disk.asm  | 15 +++++++++++++--
 src/bootloader.asm | 18 ++++++++++++++++--
 2 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/src/bios/disk.asm b/src/bios/disk.asm
index e717981..0f1b171 100644
--- a/src/bios/disk.asm
+++ b/src/bios/disk.asm
@@ -1,4 +1,5 @@
 disk_read:
+	pusha
 	push dx ; store dx on stack so that we can compare later
 
 	mov ah, BIOS_DISK_READ ; specify function
@@ -16,7 +17,8 @@ disk_read:
 	pop dx
 	cmp dh, al ; if dh != al then error
 	jne sector_error
-
+	
+	popa
 	ret
 
 sector_error:
@@ -24,13 +26,22 @@ sector_error:
 	call println
 
 read_error:
+	; Inform the user
 	mov bx, read_error_string
 	call println
 
+	; Print the error
+	mov bx, error_code_string
+	call print
+
 	mov dh, ah
 	call print_hex 
 
+	mov bx, [ASCII_END]
+	call println
+	
 	jmp $
 
-read_error_string:		db "Disk read error!", ASCII_END
+read_error_string:		db ASCII_CARRIAGE_RETURN, ASCII_LINEBREAK, "ERROR! Disk read failed.", ASCII_END
+error_code_string:		db "Error code: ", ASCII_END
 sector_error_string:	db "Invalid number of sectors read!", ASCII_END
diff --git a/src/bootloader.asm b/src/bootloader.asm
index c7d97b8..a1cab27 100644
--- a/src/bootloader.asm
+++ b/src/bootloader.asm
@@ -1,11 +1,25 @@
 [org 0x7c00] ; bootsector
+	; Save the boot drive index
+	mov [BOOT_DRIVE], dl
+
+	; Move the stack pointer somewhere safe
+	mov bp, 0x8000 ; move it to 0x8000
+	mov sp, bp
 
 	; Print the welcome string
 	mov bx, welcome_string
 	call println
 
-	; Read second sector
+	; Read second sector (outside bootsector)
+	mov bx, 0x9000			; LOAD LOCATION 
+	mov dh, 3				; SECTOR-COUNT
+	mov dl, [BOOT_DRIVE]	; DISK-INDEX
+	call disk_read
+
 
+	; Print out whatever bloated data that was read
+	mov dx, [0x9000]
+	call print_hex
 
 	jmp $  ; inf loop
 
@@ -14,7 +28,7 @@
 
 ; Data
 welcome_string:		db "e Operating-System (eOS)", ASCII_CARRIAGE_RETURN, ASCII_LINEBREAK, "Version 2021 0.0", ASCII_END
-read_test_string:	db "Read bytes: ", ASCII_END
+BOOT_DRIVE: db 0
 
 ; Bootsector
 times 510-($-$$) db 0